IOM Reports That MMR and
Thimerosal
Do Not Cause Autism

The IOM
Immunization Safety Review Committee released an updated
report on Vaccines and Autism. After careful
review of data, made available in the past 3 years, the
Committee has determined that "the body of epidemiologic
evidence favors rejection of a causal relationship
between thimerosal containing vaccines and autism.
The Committee also concluded that the body of
epidemiologic evidence favors rejection of a causal
relationship between MMR vaccine and autism." The IVS
agrees with both conclusions.

These
findings should come as no surprise to those who have
carefully followed the hypothesis that MMR may cause
autism. There has been much confusion about
thimerosal and autism. The IVS and others have raised
appropriate concerns about the safety of bolus doses of
thimerosal because methylmercury, a compound related to
the ethylmercury found in thimerosal, is a known cause
of learning disabilities in children born to women who
have consumed large quantities of fish or other seafood
contaminated with methylmercury. There is also
concern that exposure to multiple doses of ethylmercury
could be additive to the effects of methylmercury. The
EPA estimates that as many as 300,000 children are born
every year in the United States to women with levels of
methylmercury that are "of concern". The potential
effect of ethylmercury in thimerosal causing the same
mild learning disabilities as methylmercury has been
over-interpreted by some individuals as evidence that
thimerosal causes autism; a much more complex and severe
disorder.

The
IOM safety committee was asked specifically not to
review possible associations between thimerosal and mild
learning disabilities. There are ongoing
epidemiologic studies (with results expected by the end
of 2004) that should help shed light on whether or not
there is evidence of thimerosal causing learning
disabilities. However, these studies may not
address the key issue of possible additive effects
between ethylmercury and methylmercury. We
strongly encourage studies in animals to address this
key issue.